The present invention relates to an apparatus for manufacturing a semiconductor device, and more particularly to the structure of the electrodes of a three-electrode type dry etching unit.
A conventional semiconductor device manufacturing apparatus, as shown in FIG. 4(a), has an intermediate electrode 4 having a plurality of vertical through-holes 5. Of those vertical through-holes 5, the one on the straight line connecting a material to be etched and the detecting section 9 of an optical end point detecting unit 8 is made larger than the others to provide a sufficiently wide optical path, or made different in configuration from the others for the purpose of end point detection. In FIG. 4(a), reference numeral 1 designates a reaction chamber; 2, an upper electrode; 3, a lower electrode; 6, a high frequency power source; and 7, a wafer. The optical end point detecting unit 8 operates to detect with the detecting section 9 the intensity of plasma light due to an etching reaction, thereby to detect the end point of the etching.
The intermediate electrode 4, as shown in FIG. 4(b), is in the form of a disk with the through-holes 5. In the conventional apparatus, the diameter of the through-hole 5 on the straight line connecting the material to be etched and the detecting section 9 of the optical end point detecting unit is four times as large as that of the remaining through-holes 5.
Such an apparatus was used to etch a silicon oxide film under conditions and characteristics which were typically as indicated in the following Table 1:
TABLE 1 ______________________________________ Gas CHF.sub.3 100 SCCM C.sub.2 F.sub.6 40 SCCM Vacuum pressure 200 mTorr RF power 800 watts Etching speed 820 .ANG./min Uniformity 7.2% ______________________________________
The above-described conventional semiconductor device manufacturing apparatus is, however, disadvantageous in the following points: As was described above, in order to provide a sufficiently wide optical path on the straight line connecting a material to be etched and the detecting section 9 of the optical end point detecting unit 8, the corresponding through-hole 5 is made larger in diameter than the others, or it is made different in configuration from the others. Hence, the etching energy is not uniformly applied to the material to be etched, and accordingly the etching of the material is not uniform in speed and in configuration.